The present invention is particularly applicable for a single cylinder internal combustion engine used in a movable implement such as a power saw and it will be described with particular reference thereto; however, the invention has much broader applications and may be used in various internal combustion engines for a variety of purposes having a various number of control spark plugs.
In the past, the ignition system for hand implements, such as power saws, lawn mowers, snow blowers and the like, have used a magneto system wherein a rotating flywheel carries a permanent magnet which induces a voltage in the primary winding of an ignition coil. Mechanical points then open the primary winding circuit at a selected time when the induced voltage has caused a high or peak current flow. This collapses the current flow in the primary winding and causes a high voltage in the secondary winding of the ignition coil. Some prior ignition systems for small engines have used the capacitor or induction discharge concept. In the capacitor concept, a capacitor is charged to a given voltage and stores electrical energy. Mechanical points are then actuated to discharge the stored energy in the primary winding of an ignition coil. In this manner, a high sparking voltage is created in the secondary winding of the ignition coil to cause a spark at the spark plug. These types of systems have been employed in various implements driven by single cylinder internal combustion engines. These ignition systems have also been used in larger engines having more than one cylinder. In each of these instances, mechanical switching is required for creating the sparking voltage at the spark plug. Substantial effort has been made to completely eliminate mechanical switching in ignition systems, primarily for multiple cylinder internal combustion engines such as those used in motor vehicles. These systems have used a variety of solid state switching arrangements for creating a rapid change in current to induce a high voltage at the secondary winding of the ignition coil. In many of these systems, an inductive trigger is used to discharge the electrical energy. Such a trigger is operated by a moving magnetic field driven by the engine. Consequently, the speed of the engine determines the firing point which may not be the desired position for a discharge system.
The present invention relates to an improvement in the solid state ignition arrangement for a discharge system and primarily to an improvement in such a system which is beneficially used in a single cylinder engine although applicable to other types of ignition systems. The invention uses no mechanical switching for the energy discharge circuit and is operated independently of engine speed, although it may be coordinated with engine speed.